Methods of manufacting flex circuit are well known in the art. Typically, copper metalized films of polyester or polyimide on a substrate are screen printed with an etch resist over the copper film. Then the unmasked copper is etched away, and the etch resist is subsequently stripped. A protective layer is then added, exposing only areas that will be interconnected to other components or contacts.
Copper films used in the method described above, typically being 0.7 to 3.0 mils thick, require considerable amounts of etch chemicals and manufacturing time. Furthermore, the etch resist requires stripping, thereby adding additional chemistry and manufacturing time.
Sputter metallization coated polyester or polyimides are inexpensive, but are metalized too thinly (1000.ANG. to 1-micron) to provide the adequate flexible mechanical integrity needed for useful flex circuits. Additional plating would be required in order to effect any flexible mechanical integrity in a flex circuit. Despits its poor mechanical attributes, sputter metallization typically has low sheet resistances. For instance, Sputter deposited copper, depending on thickness, has a typical sheet reistance 0.1 to 5 milliohms per square.
Polymer thick film (PTF) systems, on the other hand, adequately and inexpensively provide mechanical integrity in flex circuits, but unfortunately have a high resistance. For instance, PTF has sheet resistances of 30 to 200 ohms per square, but is able to withstand millions of impacts and flexes without degradation. Reducing the resistance can be effected by loading the PTF with silver, but the cost benefits are defeated. Accordingly, a need exists for a low cost method of producing conductive patterns on a substrate utilizing the best attributes of the PTF system and the sputter metallization process, namely a low cost method of producing conductive patterns having low resistance and ruggedness to withstand many impacts and flexes.